Due to the amazing power of computer systems, computer systems are developed to have various functions. Input devices such as mouse devices, keyboards or a trackballs have been widely employed in a computer system for cursor control. Among these input devices, the mouse devices are the most prevailing because they are very easy-to-use. Typically, by rotating a roller of the mouse device, the image shown on the display screen may be scrolled upwardly and downwardly. The rollers for use in the mouse devices are usually classified into two types, i.e. a clicking-feel-imparting type and a clicking-feel-lacking type. When the clicking-feel-imparting type roller is rotated with a user's finger, the feeling of smooth clicks is imparted to the user. Whereas, rotation of the clicking-feel-lacking type roller gives no feeling of smooth clicks.
When the clicking-feel-imparting type roller is rotated for a graduation, the image is scrolled by a specified increment. For example, when the clicking-feel-imparting type roller is rotated for a graduation, the image shown on the display screen may be scrolled by a line, several lines or a page. As a consequence, the user is obviously conscious of the scrolled images upon rotating of the roller. In contrast, rotation of the clicking-feel-lacking type roller gives no feeling of smooth clicks.
The clicking-feel-imparting type roller and the clicking-feel-lacking type roller have their respective characters. The clicking-feel-imparting type roller is feasible in some instances, and the clicking-feel-lacking type roller is feasible in some other instances. So far, the commercial available mouse devices have either the clicking-feel-imparting type rollers or the clicking-feel-lacking type rollers. That is, the existing mouse devices have no means of operating the rollers in the clicking-feel-imparting mode or the clicking-feel-lacking mode according to the user's requirement.